Modified cutters and a method of drilling with modified cutters

ABSTRACT

A cutter for a drag bit may include a substrate and an ultrahard layer on an end surface of the substrate. The ultrahard layer may include an exposed surface having at least three depressions extending from an interior of the exposed surface radially outward to a peripheral edge formed between the working surface and a side surface of the ultrahard layer, the at least three depressions separated from each other by at least three raised regions forming an apex of the exposed surface, the at least three raised regions connected to each other proximate the central axis and extending from proximate the central axis to the peripheral edge. Other working surfaces are also included.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/180,121, filed on Feb. 13, 2014, which is a broadening reissue ofU.S. application Ser. No. 12/796,560, filed on Jun. 8, 2010, issued asU.S. Pat. No. 8,113,303 on Feb. 14, 2012, which is a continuation ofU.S. application Ser. No. 11/855,770, filed Sep. 14, 2007 issued as U.S.Pat. No. 7,757,785 on Jul. 20, 2010, which is a continuation of U.S.patent application Ser. No. 11/117,647, filed Apr. 28, 2005, nowabandoned, which claims priority, pursuant to 35 U.S.C. §119(e), to U.S.Provisional Patent Application No. 60/648,863, filed Feb. 1, 2005, U.S.Provisional Patent Application No. 60/584,307 filed Jun. 30, 2004, andU.S. Provisional Patent Application No. 60/566,751 filed Apr. 30, 2004.These applications are incorporated herein by reference in theirentireties.

BACKGROUND

1. Technical Field

The disclosure relates generally to modified cutters.

2. Background Art

Rotary drill bits with no moving elements on them are typically referredto as “drag” bits. Drag bits are often used to drill a variety of rockformations. Drag bits include those having cutters (sometimes referredto as cutter elements, cutting elements or inserts) attached to the bitbody. For example, the cutters may be formed having a substrate orsupport stud made of cemented carbide, for example tungsten carbide, andan ultra hard cutting surface layer or “table” made of a polycrystallinediamond material or a polycrystalline boron nitride material depositedonto or otherwise bonded to the substrate at an interface surface.

An example of a prior art drag bit having a plurality of cutters withultra hard working surfaces is shown in FIG. 1. The drill bit 10includes a bit body 12 and a plurality of blades 14 that are formed onthe bit body 12. The blades 14 are separated by channels or gaps 16 thatenable drilling fluid to flow between and both clean and cool the blades14 and cutters 18. Cutters 18 are held in the blades 14 at predeterminedangular orientations and radial locations to present working surfaces 20with a desired back rake angle against a formation to be drilled.Typically, the working surfaces 20 are generally perpendicular to theaxis 19 and side surface 21 of a cylindrical cutter 18. Thus, theworking surface 20 and the side surface 21 meet or intersect to form acircumferential cutting edge 22.

Nozzles 23 are typically formed in the drill bit body 12 and positionedin the gaps 16 so that fluid can be pumped to discharge drilling fluidin selected directions and at selected rates of flow between the cuttingblades 14 for lubricating and cooling the drill bit 10, the blades 14and the cutters 18. The drilling fluid also cleans and removes thecuttings as the drill bit rotates and penetrates the geologicalformation. The gaps 16, which may be referred to as “fluid courses,” arepositioned to provide additional flow channels for drilling fluid and toprovide a passage for formation cuttings to travel past the drill bit 10toward the surface of a wellbore (not shown).

The drill bit 10 includes a shank 24 and a crown 26. Shank 24 istypically formed of steel or a matrix material and includes a threadedpin 28 for attachment to a drill string. Crown 26 has a cutting face 30and outer side surface 32. The particular materials used to form drillbit bodies are selected to provide adequate toughness, while providinggood resistance to abrasive and erosive wear. For example, in the casewhere an ultra hard cutter is to be used, the bit body 12 may be madefrom powdered tungsten carbide (WC) infiltrated with a binder alloywithin a suitable mold form. In one manufacturing process the crown 26includes a plurality of holes or pockets 34 that are sized and shaped toreceive a corresponding plurality of cutters 18.

The combined plurality of surfaces 20 of the cutters 18 effectivelyforms the cutting face of the drill bit 10. Once the crown 26 is formed,the cutters 18 are positioned in the pockets 34 and affixed by anysuitable method, such as brazing, adhesive, mechanical means such asinterference fit, or the like. The design depicted provides the pockets34 inclined with respect to the surface of the crown 26. The pockets 34are inclined such that cutters 18 are oriented with the working face 20at a desired rake angle in the direction of rotation of the bit 10, soas to enhance cutting. It will be understood that in an alternativeconstruction (not shown), the cutters can each be substantiallyperpendicular to the surface of the crown, while an ultra hard surfaceis affixed to a substrate at an angle on a cutter body or a stud so thata desired rake angle is achieved at the working surface.

A typical cutter 18 is shown in FIG. 2. The typical cutter 18 has acylindrical cemented carbide substrate body 38 having an end face orupper surface 54 referred to herein as the “interface surface” 54. Anultra hard material layer (cutting layer) 44, such as polycrystallinediamond or polycrystalline cubic boron nitride layer, forms the workingsurface 20 and the cutting edge 22. A bottom surface 52 of the cuttinglayer 44 is bonded on to the upper surface 54 of the substrate 38. Thejoining surfaces 52 and 54 are herein referred to as the interface 46.The top exposed surface or working surface 20 of the cutting layer 44 isopposite the bottom surface 52. The cutting layer 44 typically has aflat or planar working surface 20, but may also have a curved exposedsurface, that meets the side surface 21 at a cutting edge 22.

Cutters may be made, for example, according to the teachings of U.S.Pat. No. 3,745,623, whereby a relatively small volume of ultra hardparticles such as diamond or cubic boron nitride is sintered as a thinlayer onto a cemented tungsten carbide substrate. Flat top surfacecutters as shown in FIG. 2 are generally the most common and convenientto manufacture with an ultra hard layer according to known techniques.It has been found that cutter chipping, spalling and delamination arecommon failure modes for ultra hard flat top surface cutters.

Generally speaking, the process for making a cutter 18 employs a body ofcemented tungsten carbide as the substrate 38, wherein the tungstencarbide particles are cemented together with cobalt. The carbide body isplaced adjacent to a layer of ultra hard material particles such asdiamond or cubic boron nitride particles and the combination issubjected to high temperature at a pressure where the ultra hardmaterial particles are thermodynamically stable. This results inrecrystallization and formation of a polycrystalline ultra hard materiallayer, such as a polycrystalline diamond or polycrystalline cubic boronnitride layer, directly onto the upper surface 54 of the cementedtungsten carbide substrate 38.

It has been found by applicants that many cutters develop cracking,spalling, chipping and partial fracturing of the ultra hard materialcutting layer at a region of cutting layer subjected to the highestloading during drilling. This region is referred to herein as the“critical region” 56. The critical region 56 encompasses the portion ofthe cutting layer 44 that makes contact with the earth formations duringdrilling. The critical region 56 is subjected to the generation of highmagnitude stresses from dynamic normal loading, and shear loadingsimposed on the ultra hard material layer 44 during drilling. Because thecutters are typically inserted into a drag bit at a rake angle, thecritical region includes a portion of the ultra hard material layer nearand including a portion of the layer's circumferential edge 22 thatmakes contact with the earth formations during drilling.

The high magnitude stresses at the critical region 56 alone or incombination with other factors, such as residual thermal stresses, canresult in the initiation and growth of cracks 58 across the ultra hardlayer 44 of the cutter 18. Cracks of sufficient length may cause theseparation of a sufficiently large piece of ultra hard material,rendering the cutter 18 ineffective or resulting in the failure of thecutter 18. When this happens, drilling operations may have to be ceasedto allow for recovery of the drag bit and replacement of the ineffectiveor failed cutter. The high stresses, particularly shear stresses, canalso result in delamination of the ultra hard layer 44 at the interface46.

One type of ultra hard working surface 20 for fixed cutter drill bits isformed as described above with polycrystalline diamond on the substrateof tungsten carbide, typically known as a polycrystalline diamondcompact (PDC), PDC cutters, PDC cutting elements, or PDC inserts. Drillbits made using such PDC cutters 18 are known generally as PDC bits.While the cutter or cutter insert 18 is typically formed using acylindrical tungsten carbide “blank” or substrate 38 which issufficiently long to act as a mounting stud 40, the substrate 38 mayalso be an intermediate layer bonded at another interface to anothermetallic mounting stud 40.

The ultra hard working surface 20 is formed of the polycrystallinediamond material, in the form of a cutting layer 44 (sometimes referredto as a “table”) bonded to the substrate 38 at an interface 46. The topof the ultra hard layer 44 provides a working surface 20 and the bottomof the ultra hard layer cutting layer 44 is affixed to the tungstencarbide substrate 38 at the interface 46. The substrate 38 or stud 40 isbrazed or otherwise bonded in a selected position on the crown of thedrill bit body 12 (FIG. 1). As discussed above with reference to FIG. 1,the PDC cutters 18 are typically held and brazed into pockets 34 formedin the drill bit body at predetermined positions for the purpose ofreceiving the cutters 18 and presenting them to the geological formationat a rake angle.

In order for the body of a drill bit to be resistant to wear, hard andwear-resistant materials such as tungsten carbide are typically used toform the drill bit body for holding the PDC cutters. Such a drill bitbody is very hard and difficult to machine. Therefore, the selectedpositions at which the PDC cutters 18 are to be affixed to the bit body12 are typically formed during the bit body molding process to closelyapproximate the desired final shape. A common practice in molding thedrill bit body is to include in the mold, at each of the to-be-formedPDC cutter mounting positions, a shaping element called a“displacement.”

A displacement is generally a small cylinder, made from graphite orother heat resistant materials, which is affixed to the inside of themold at each of the places where a PDC cutter is to be located on thefinished drill bit. The displacement forms the shape of the cuttermounting positions during the bit body molding process. See, forexample, U.S. Pat. No. 5,662,183 issued to Fang for a description of theinfiltration molding process using displacements.

It has been found by applicants that cutters with sharp cutting edges orsmall back rake angles provide a good drilling ROP, but are oftensubject to instability and are susceptible to chipping, cracking orpartial fracturing when subjected to high forces normal to the workingsurface. For example, large forces can be generated when the cutter“digs” or “gouges” deep into the geological formation or when suddenchanges in formation hardness produce sudden impact loads. Small backrake angles also have less delamination resistance when subjected toshear load. Cutters with large back rake angles are often subjected toheavy wear, abrasion and shear forces resulting in chipping, spalling,and delamination due to excessive downward force or weight on bit (WOB)required to obtain reasonable ROP. Thick ultra hard layers that might begood for abrasion wear are often susceptible to cracking, spalling, anddelamination as a result of residual thermal stresses associated withforming thick ultra hard layers on the substrate. The susceptibility tosuch deterioration and failure mechanisms is accelerated when combinedwith excessive load stresses.

FIG. 3 shows a prior art PDC cutter held at an angle in a drill bit 10for cutting into a formation 45. The cutter 18 includes a diamondmaterial table 44 affixed to a tungsten carbide substrate 38 that isbonded into the pocket 34 formed in a drill bit blade 14. The drill bit10 (see FIG. 1) will be rotated for cutting the inside surface of acylindrical well bore. Generally speaking, the back rake angle “A” isused to describe the working angle of the working surface 20, and italso corresponds generally to the magnitude of the attack angle “B” madebetween the working surface 20 and an imaginary tangent line at thepoint of contact with the well bore. It will be understood that the“point” of contact is actually an edge or region of contact thatcorresponds to critical region 56 (see FIG. 2) of maximum stress on thecutter 18. Typically, the geometry of the cutter 18 relative to the wellbore is described in terms of the back rake angle “A.”

Different types of bits are generally selected based on the nature ofthe geological formation to be drilled. Drag bits are typically selectedfor relatively soft formations such as sands, clays and some soft rockformations that are not excessively hard or excessively abrasive.However, selecting the best bit is not always straightforward becausemany formations have mixed characteristics (i.e., the geologicalformation may include both hard and soft zones), depending on thelocation and depth of the well bore. Changes in the geological formationcan affect the desired type of a bit, the desired ROP of a bit, thedesired rotation speed, and the desired downward force or WOB. Where adrill bit is operated outside the desired ranges of operation, the bitcan be damaged or the life of the bit can be severely reduced.

For example, a drill bit normally operated in one general type offormation may penetrate into a different formation too rapidly or tooslowly subjecting it to too little load or too much load. For anotherexample, a drill bit rotating and penetrating at a desired speed mayencounter an unexpectedly hard formation material, possibly subjectingthe bit to a “surprise” or sudden impact force. A formation materialthat is softer than expected may result in a high rate of rotation, ahigh ROP, or both, that can cause the cutters to shear too deeply or togouge into the geological formation.

This can place greater loading, excessive shear forces and added heat onthe working surface of the cutters. Rotation speeds that are too highwithout sufficient WOB, for a particular drill bit design in a givenformation, can also result in detrimental instability (bit whirling) andchattering because the drill bit cuts too deeply or intermittently bitesinto the geological formation. Cutter chipping, spalling, anddelamination, in these and other situations, are common failure modesfor ultra hard flat top surface cutters.

Dome cutters have provided certain benefits against gouging and theresultant excessive impact loading and instability. This approach forreducing adverse effects of flat surface cutters is described in U.S.Pat. No. 5,332,051. An example of such a dome cutter in operation isdepicted in FIG. 4. The prior art cutter 60 has a dome shaped top orworking surface 62 that is formed with an ultra hard layer 64 bonded toa substrate 66. The substrate 66 is bonded to a metallic stud 68. Thecutter 60 is held in a blade 70 of a drill bit 72 (shown in partialsection) and engaged with a geological formation 74 (also shown inpartial section) in a cutting operation. The dome shaped working surface62 effectively modifies the rake angle A that would be produced by theorientation of the cutter 60.

Scoop cutters, as shown at 80 in FIG. 5 (U.S. Pat. No. 6,550,556), havealso provided some benefits against the adverse effects of impactloading. This type of prior art cutter 80 is made with a “scoop” ordepression 90 formed in the top working surface 82 of an ultra hardlayer 84. The ultra hard layer 84 is bonded to a substrate 86 at aninterface 88. The depression 90 is formed in the critical region 56. Theupper surface 92 of the substrate 86 has a depression 94 correspondingto the depression 90, such that the depression 90 does not make theultra hard layer 84 too thin. The interface 88 may be referred to as anon-planar interface (NPI).

What is still needed, however, are improved cutters for use in a varietyof applications.

SUMMARY

In one aspect, the present disclosure relates to a modified cuttingelement that includes a base portion, an ultrahard layer disposed onsaid base portion, and at least one modified region disposed adjacent toa cutting face of the cutter.

In one aspect, the present disclosure relates to a drill bit thatincludes a bit body; and at least one cutter, the at least one cuttercomprising a base portion, an ultrahard layer disposed on said baseportion, and at least one modified region disposed adjacent to a cuttingface of the cutter.

Other aspects and advantages of the disclosure will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a prior art fixed cutter drill bitsometimes referred to as a “drag bit”;

FIG. 2 is a perspective view of a prior art cutter or cutter insert withan ultra hard layer bonded to a substrate or stud;

FIG. 3 is a partial section view of a prior art flat top cutter held ina blade of a drill bit engaged with a geological formation (shown inpartial section) in a cutting operation;

FIG. 4 is a schematic view of a prior art dome top cutter with an ultrahard layer bonded to a substrate that is bonded to a stud, where thecutter is held in a blade of a drill bit (shown in partial section) andengaged with a geological formation (also shown in partial section) in acutting operation;

FIG. 5 is a perspective view of a prior art scoop top cutter with anultra hard layer bonded to a substrate at a non-planar interface (NPI);

FIGS. 6A, 6B, and 6C show a side, front, and perspective view of acutter in accordance with an embodiment of the present invention;

FIG. 7 shows a cutter in accordance with another embodiment of thepresent invention; and

FIG. 8 shows a blade including cutters in accordance with an embodimentof the present invention.

FIG. 9 shows a PDC bit including cutters formed in accordance with anembodiment of the present invention.

FIGS. 10A, 10B, and 10C are perspective and cross-sectional views of anultra hard top layer having a varied geometry chamfer circumferentiallyaround the cutting edge of the working surface of the ultra hard layerwherein the size of the chamfer is varied circumferentially around thecutting edge according to one embodiment;

FIG. 11 is a graph showing the average chamfer size as varied withdifferent cutting depths for a cutter having varied chamfer as comparedto a cutter having fixed geometry chamfer.

FIG. 12 shows an ultra hard layer according to one or more embodiments.

FIG. 13 shows a cutter according to one or more embodiments.

DETAILED DESCRIPTION

The present disclosure relates to shaped cutters that provide advantageswhen compared to prior art cutters. In particular, embodiments of thepresent disclosure relate to cutters that have structural modificationsto the cutting surface in order to improve cutter performance. As aresult of the modifications, embodiments of the present disclosure mayprovide improved cooling, higher cutting efficiency, and longer lastingcutters when compared with prior art cutters.

Embodiments of the present disclosure relate to cutters having asubstrate or support stud, which in some embodiments may be made ofcemented carbide, for example tungsten carbide, and an ultra hardcutting surface layer or “table” made of a polycrystalline diamondmaterial or a polycrystalline boron nitride material deposited onto orotherwise bonded to the substrate at an interface surface. Also, inselected embodiments, the ultra-hard layer may comprise a “thermallystable” layer. One type of thermally stable layer that may be used inembodiments of the present disclosure is leached polycrystallinediamond.

A typical polycrystalline diamond layer includes individual diamond“crystals” that are interconnected. The individual diamond crystals thusform a lattice structure. A metal catalyst, such as cobalt may be usedto promote recrystallization of the diamond particles and formation ofthe lattice structure. Thus, cobalt particles are typically found withinthe interstitial spaces in the diamond lattice structure. Cobalt has asignificantly different coefficient of thermal expansion as compared todiamond. Therefore, upon heating of a diamond table, the cobalt and thediamond lattice will expand at different rates, causing cracks to formin the lattice structure and resulting in deterioration of the diamondtable.

In order to obviate this problem, strong acids may be used to “leach”the cobalt from the diamond lattice structure. Examples of “leaching”processes can be found, for example in U.S. Pat. Nos. 4,288,248 and4,104,344. Briefly, a hot strong acid, e.g., nitric acid, hydrofluoricacid, hydrochloric acid, or perchloric acid, or combinations of severalstrong acids may be used to treat the diamond table, removing at least aportion of the catalyst from the PDC layer.

Removing the cobalt causes the diamond table to become more heatresistant, but also causes the diamond table to be more brittle.Accordingly, in certain cases, only a select portion (measured either indepth or width) of a diamond table is leached, in order to gain thermalstability without losing impact resistance. As used herein, thermallystable polycrystalline diamond compacts include both of the above (i.e.,partially and completely leached) compounds. In one embodiment, only aportion of the polycrystalline diamond compact layer is leached. Forexample, a polycrystalline diamond compact layer having a thickness of0.010 inches may be leached to a depth of 0.006 inches. In otherembodiments, the entire polycrystalline diamond compact layer may beleached. A number of leaching depths may be used, depending on theparticular application, for example, in one embodiment the leachingdepth may be 0.05 mm.

FIGS. 6A-6C show multiple views of a cutter formed in accordance with anembodiment of the present invention. In FIG. 6A, a cutter comprises asubstrate or “base portion,” 600, on which an ultrahard layer 602 isdisposed. In this embodiment, the ultrahard layer 602 comprises apolycrystalline diamond layer. As explained above, when apolycrystalline diamond layer is used, the layer may further bepartially or completely leached. A beveled edge 606 may be provided onat least one side of the ultrahard layer 602, but more commonly, may beplaced on at least two sides, so that the cutter may be removed andreoriented for use a second time. Further, at least one modified region604 is formed on the ultrahard layer 602. FIGS. 6B and 6C show that, inthis embodiment, two modified regions 604 have been formed on theultrahard layer 602. In particular, in FIG. 6C the modified regions 604comprise tapered portions that have been machined from the ultrahardlayer 602.

The original height of the diamond table layer is shown as unmodifiedportion 608, as the modified regions 604 are designed such that theunmodified portion 608 has a discrete width in this embodiment. In someinstances the modified region or regions 604 may be formed when thecutter is actually being bonded together (i.e., a modified region isoriginally built into the ultrahard layer), but in other instances, themodified region may be formed after the formation of the ultrahardlayer, by using electrical discharge machining, for example. Inaddition, in select embodiments, only portions of the modified surfacemay be leached. Those having ordinary skill in the art will recognizethat masking agents may be used to prevent leaching in certain areas, toprovide regions that are leached and legions that are unleached.

Wire electrical discharge machining (EDM) is an electrical dischargemachining process with a continuously moving conductive wire as toolelectrode. The mechanism of metal removal in wire EDM involves thecomplex erosion effect of electric sparks generated by a pulsatingdirect current power supply between two closely spaced electrodes indielectric liquid. The high energy density erodes material from both thewire and workpiece by local melting and vaporizing. Because the new wirekeeps feeding to the machining area, the material is removed from theworkpiece with the moving of wire electrode. Eventually, a cutting shapeis formed on the workpiece by the programmed moving trajectory of wireelectrode.

As the term is used herein, a modified region constitutes at least onearea, adjacent to the cutting face, that has a lower overall height thanthe cutting face itself. Cutters containing the modified region 604 havea number of advantages when compared to prior art planar cutters. Forexample, because the modified region is a depressed area adjacent to thecutting face, improved cooling (due to better fluid flow and/or airflow) around the cutting edge may be seen, which may help preventfailure due to thermal degradation.

In the embodiment shown in FIG. 6 c, the beveled edge 606 is formed suchthat when placed into a pocket, the beveled edge 606 will form thecutting face of the cutter. Those having ordinary skill in the art willappreciate that the size of the beveled edge may be modified dependingon the application. For example, in selected applications, the size mayrange from five thousandths of an inch (0.005 inches) to about fiftythousandths of an inch (0.050 inches). In addition, the bevel may belocated at other portions, or additional beveled regions may beprovided. In selected embodiments, the modified region 604 is providedsuch that a self-sharpening effect occurs at the cutting face. That is,as portions of the cutter chip away, a fresh portion is exposed. Havingthis self-sharpening beveled edge 606 may provide higher cuttingefficiency as compared to prior art cutters, as the beveled edge mayinitially fracture rock more efficiently than a typical planar contact.This feature may be particularly useful in higher hardness formations.Embodiments may also include cutters having shaped working surfaces witha varied geometry chamfer. Referring now to FIG. 10A, FIG. 10A shows anultra hard top layer 800 for a cutter that has a shaped working surface102 including a varied geometry chamfer 104 circumferentially around thecutting edge 106. The bevel 104 is varied in size circumferentiallyaround the cutting edge 106 according to one embodiment. The change inthe size or the width of the bevel is demonstrated in the elevationsection views of FIGS. 10B and 10C taken along section lines B-B and C-Cof FIG. 1 OA, respectively. In this embodiment, the width 108 in FIG.10B is smaller than the width 110 in FIG. 10C. The angle 112 of thebevel at section B-B, FIG. 10B, is the same as angle 114 at section lineC-C, FIG. 10C; however, in other embodiments, the angle of the bevel isvaried circumferentially around the cutting edge. It will be understoodthat a varied geometry of a bevel could also be provided as acombination of varied size and varied angle. Additionally, in one ormore embodiments, the bevel is formed so that its size increases awayfrom the area of the cutter surface engaged with the geologicalformation. For example, referring to FIG. 11, the amount of the variablesize bevel in contact with the formation increases with the depth ofcut. Thus, when the cutter digs into the formation, a greater portion ofthe cutting edge has a larger bevel to give more protection againstchipping and spalling.

In FIG. 7, another embodiment of the present invention is shown. In FIG.7, a cutter 700, is shown having a base portion 702 and a ultrahardlayer 704 disposed thereon. Further, a beveled edge 706 is provided at acutting face of the insert. In this embodiment, a modified region 708extends over substantially all of the cutter 700. In this embodiment,the modified region 708 comprises a substantially continuous “saddleshaped” region. In this embodiment, if the modified region is formedafter the deposition of an ultrahard layer, the modified region may beformed in a single manufacturing pass, whereas with the multiplemodified regions in FIGS. 6A, 6B, and 6C, multiple manufacturing passesmay be required. As can be seen from FIG. 7, the ultrahard materiallayer has an exposed upper surface 710 and a peripheral surface 712,such that the upper surface intersects the peripheral surface along aperipheral edge 714. As can be seen, the peripheral edge 714continuously decreases in height and increases in height as measuredfrom a first plane 716 perpendicular to a longitudinal axis 718. Theperipheral edge decreases from a maximum height 719 as measured from aplane 716 to a minimum height of 720 as measured from the same plane716. As second plane 722 along the longitudinal axis 718 intersects theperipheral edge at a first point 724 and a second point 726. A thirdplane 728 along the longitudinal axis 718 insects the peripheral edge ata third point 730 and a fourth point 732. As can be seen from FIG. 7,the peripheral edge has a first convex portion 740 extending from thefirst point 724 in a direction towards the third point 730. In addition,a first concave portion 742 extends from the first convex portion 740 tothe third point 730. Similarly, a second concave portion extends fromthe third point in a direction towards the second point 726 and a secondconvex portion extends from the second concave portion to the secondpoint 726. Moreover, a third convex portion extends from the secondpoint 726 in a direction towards the fourth point 732 and a thirdconcave portion extends from the third convex portion to the fourthpoint 732. In addition, a fourth concave point extends from the fourthpoint 732 in a direction towards the first point 724 and a fourth convexportion extends from the fourth concave portion to the first point 724.

After formation of the saddle-shaped cutter, mill tests were performedto determine the performance of the cutters. Test results showed thatapproximately a 20% increase in performance when compared to prior artcutters was seen when a polycrystalline diamond surface was used. Inaddition, when thermally stable polycrystalline diamond was used as theultrahard layer, a performance jump of nearly 70% was seen as comparedto unmodified thermally stable polycrystalline diamond cutters. Asstated above, without being limited to any particular theory, that theimproved performance may be due to a number of factors such as, improvedcooling around the cutting face, higher cutting efficiency (due to thenon-planar interaction at the cutting face), and the fact that anon-planar interface leads to less flaking of the thermally stablepolycrystalline diamond.

Cutters formed in accordance with embodiments of the present inventionmay be used either alone or in conjunction with standard cuttersdepending on the desired application. In addition, while reference hasbeen made to specific manufacturing techniques, those of ordinary skillwill recognize that any number of techniques may be used.

FIG. 8 shows a view of cutters formed in accordance with embodiments ofthe present invention disposed on a blade of a PDC bit. In FIG. 8,modified cutters 804 are intermixed on a blade 800 with standard cutters802. Similarly, FIG. 9 shows a PDC bit having modified cutters 904disposed thereon. Referring to FIG. 9, the fixed-cutter bits (alsocalled drag bits) 900 comprise a bit body 902 having a threadedconnection at one end 903 and a cutting head 906 formed at the otherend. The head 906 of the fixed-cutter bit 900 comprises a plurality ofblades 908 arranged about the rotational axis of the bit and extendingradially outward from the bit body 902. Modified cutting elements 904are embedded in the blades 908 to cut through earth formation as the bitis rotated on the earth formation. As discussed above, the modifiedcutting elements may be mixed with standard cutting elements 905.

FIG. 12 shows another embodiment of an ultra hard top layer 140 for acutter with a shaped working surface 142 and having a varied geometrychamfer 144 circumferentially around a cutting edge 146 at theintersection of the shaped working surface 142 and a side surface 148.The shaped working surface 142 includes one or more depressions 150 a,150 b, and 150 c extending radially outwardly to the cutting edge 146.While three depressions 150 a-c are depicted uniformly spaced around theshaped working surface 142, fewer or a greater number with uniform ornon-uniform spacing may be formed without departing from certain aspectsof the disclosure. For example, one or more depressions 150 a-c can beformed as one or more planar surfaces or facets in a face 154.

Depending upon the embodiment, the face 154 may be a planar shapedsurface, a dome shaped surface or a surface having another shape. Thedepressions 150 a-c in this embodiment comprise planar surfaces orfacets each at an obtuse angle relative to a central axis 152 of thecylindrical ultra hard top layer. The obtuse angle is different from theangle of other portions of the working surface, such that a relativedepressed area defining the depressions 150 a-c is formed the face 154.Where the surrounding portions of the face 154 are planar and at a90-degree angle with respect to the axis of the cutter, the obtuse angleis generally greater than 90 degrees with respect to the axis 152 of thecutter. However, according to alternative embodiments of the invention,the obtuse angle may be less than 90 degrees. It will also be understoodthat in other alternative embodiments, each of the depressions 150 a-ccan be multi-faceted or comprised of multiple planar surfaces.Alternatively, the depressions 150 a-c can also be formed with simplecurved surfaces that may be concave or convex or can be formed with aplurality of curved surfaces or with a smooth complex curve.

The depressions 150 a-c may be formed and shaped during the initialcompaction of the ultra hard layer 140 or can be shaped after the ultrahard layer is formed, for example by Electro Discharge Machining (EDM)or by Electro Discharge Grinding (EDG). The ultra hard layer 140 may,for example, be formed as a polycrystalline diamond compact or apolycrystalline cubic boron nitride compact. Also, in selectedembodiments, the ultra-hard layer may comprise a “thermally stable”layer. One type of thermally stable layer that may be used inembodiments may be a TSP element or partially or fully leachedpolycrystalline diamond. The depressions 150 a-c extend generally at anangle relative to the face 154 outward to the edge of the cutter. It hasbeen found that a varied chamfer 144 can be conveniently made with afixed angle and fixed depth EDM or EDG device. For example, an EDMdevice will typically cut deepest into the edge 146 where the raiseareas of face 154 extend to the edge 146 and will cut less deep wherethe depressions 150 a-c extend to the edge 146. The chamfer 144 is cutthe least at the lowest edge point in each depression 150 a-c andprogressively deeper on either side of the lowest edge point. A variedwidth or size chamfer is conveniently formed circumferentially aroundthe edge 146 of the ultra hard cutter layer 140. Alternatively, variableor programmable angle and depth EDM or EGM can be used to form thevariable geometry chamfer. FIG. 13 shows a three-dimensional model of acutter 160 having an ultra hard layer 162 with a shaped working surface164. The ultra hard layer 162 is bonded to a substrate 166 at anon-planar interface 168 according to one embodiment of the invention.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed:
 1. A cutter, comprising: a substrate; and an ultrahardlayer on an end surface of the substrate, the ultrahard layer includinga central axis and an exposed surface having at least three depressionsextending from an interior of the exposed surface radially outward to aperipheral edge formed between the working surface and a side surface ofthe ultrahard layer, the at least three depressions separated from eachother by at least three raised regions forming an apex of the exposedsurface, the at least three raised regions connected to each otherproximate the central axis and extending from proximate the central axisto the peripheral edge.
 2. The cutter of claim 1, wherein at least oneraised region has a width that varies on a length of the raised region.3. The cutter of claim 1, wherein the peripheral edge undulates betweenthe at least three raised regions and the at least three depressions. 4.The cutter of claim 1, wherein the peripheral edge extends to an outerdiameter of the cutter.
 5. The cutter of claim 1, wherein the at leastthree raised ridges comprise a flat region extending from a firstportion of the peripheral edge to the central axis.
 6. The cutter ofclaim 1, wherein the at least three depressions have a concavecurvature.
 7. The cutter of claim 1, wherein the apex comprises a convexcurvature.
 8. The cutter of claim 1, wherein the peripheral edge has avaried geometry around at least a portion of the periphery of theexposed top surface.
 9. A fixed cutter drill bit comprising a bodyhaving the cutter as recited in claim 1 mounted thereon.
 10. A cutterfor a drag bit, the cutter comprising: a substrate; an ultrahard layeron an end surface of the substrate, the ultrahard layer including anexposed top surface surrounded by a peripheral edge, the exposed topsurface comprising: an apex extending from the first cutting edge toanother portion of the peripheral edge, wherein the exposed top surfacedecreases in height away from the apex to other portions of theperipheral edge which have a lower overall height than the height of theapex, wherein the apex has a width that varies along its length.
 11. Thecutter of claim 10, wherein the apex comprises a convex curvature. 12.The cutter of claim 10, wherein the exposed top surface has a concavecurvature as it decreases in height away from the apex.
 13. The cutterof claim 10, wherein the peripheral edge has a varied geometry around atleast a portion of the periphery of the exposed top surface.
 14. Thecutter of claim 10, wherein the apex comprises a flat region extendingfrom the first cutting edge to the other portion of the peripheral edge.15. A fixed cutter drill bit comprising a body having the cutter asrecited in claim 10 mounted thereon.
 16. A cutter, comprising: asubstrate; an ultrahard layer on an end surface of the substrate, theultrahard layer including an exposed dome shaped top surface surroundedby a peripheral edge, the dome shaped exposed top surface comprising: anapex extending from the first cutting edge to another portion of theperipheral edge, wherein the exposed top surface decreases in heightaway from the apex to other portions of the peripheral edge which have alower overall height than the height of the apex.
 17. The cutter ofclaim 16, wherein the apex comprises a convex curvature.
 18. The cutterof claim 16, wherein the exposed top surface has a concave curvature asit decreases in height away from the apex.
 19. The cutter of claim 16,wherein the peripheral edge has a varied geometry around at least aportion of the periphery of the exposed top surface.
 20. A fixed cutterdrill bit comprising a body having the cutter as recited in claim 16mounted thereon.